Technical Field
The present invention relates to a laser heterodyne interferometric straightness measurement apparatus and method, and more particularly, to a laser heterodyne interferometric straightness measurement apparatus and method with six degrees of freedom (DOFs) determination.
Description of Related Art
Straightness, as one of the main geometric elements of stages or guide rails in the manufacturing of modern precision machinery and instruments, plays an important role in the testing of mechanical accuracy. At present, many straightness measurement methods are available and these methods can be divided into the laser measurement and the non-laser measurement by whether laser is used as the measurement carrier. The former can provide higher measurement accuracy and is easier to conduct compared with the later, and it has always been the main study subject of scholars and enterprises at home and abroad. Among the laser measurement, the laser heterodyne straightness interferometer is widely applied in the field of straightness measurement for its favorable characteristics, such as good anti-interference, high signal-to-noise ratio and high accuracy. The laser heterodyne straightness interferometer mainly comprises a dual-frequency laser, a Wollaston prism and a V-shaped retroreflector and generally determines one DOF parameter of straightness error of a measured object only. Chinese invention patents under grants No. 200910100065.2 and No. 200910100068.6 have realized the determination of two DOF parameters of straightness error and its position of a measured object by using of the optical path configuration of a nonpolarizing beam-splitter, a Wollaston prism, a V-shaped retroreflector and a polarizing beam-splitter.
In actual straightness measurement, the measuring retroreflector of a laser heterodyne straightness interferometer is mounted on the movable platform of a measured object. The platform has six DOFs error parameters during the motion, including three linear parameters (vertical straightness error, horizontal straightness error and position of straightness error) and three rotational parameters (yaw angle error, pitch angle error and roll angle error), wherein the three rotational errors will affect the measurement results of the straightness error and its position greatly and then decrease the measurement accuracy. Therefore, current laser heterodyne interferometric straightness measurement apparatuses and methods have such technical problems as incapability of eliminating the influence of these rotational errors on the straightness measurement result, and cannot realize the simultaneous determination of six DOFs error parameters of a measured object.